Endoscope and endoscopic system

ABSTRACT

Disclosed is an endoscope including: a four-color separation prism configured to separate light from an object into three primary colors of light and infrared light; four image sensors configured to convert optical images of the separated three primary colors of light and an optical image of the separated infrared light into electrical signals; and an output device configured to output the converted electrical signals.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This disclosure relates to an endoscope and an endoscopic system.

2. Description of the Related Art

In the related art, an endoscopic system in which a three-colorseparation prism is used is known. An endoscopic system disclosed inJapanese Patent Unexamined Publication No. 2013-116353 acquires acaptured color image in which a site in the body is expressed in acombination of three colors, that is, red (R), green (G), and blue (B),and performs image processing on the captured image to emphasize thedesignated wavelength component.

Meanwhile, when an IR light (infrared light) component is added to animage in addition to the three R, G, and B colors, the image quality ofthe image captured by an endoscope is not good enough in the endoscopicsystem disclosed in Japanese Patent Unexamined Publication No.2013-116353.

SUMMARY OF THE INVENTION

This disclosure is made in light of this problem, and provides anendoscope and an endoscopic system by which it is possible to improveimage quality to which an infrared light component is added.

According to an aspect of this disclosure, there is provided anendoscope including: a four-color separation prism configured toseparate light from an object into three primary colors of light andinfrared light; four image sensors configured to convert optical imagesof the separated three primary colors of light and an optical image ofthe separated infrared light into electrical signals; and an outputdevice configured to output the converted electrical signals.

According to this disclosure, it is possible to improve the imagequality of an image to which an infrared light component is added andwhich is captured by an endoscope.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an exterior view illustrating an example of an endoscope in afirst exemplary embodiment of this disclosure;

FIG. 2 is a schematic view illustrating an example of the configurationof the endoscope;

FIG. 3 is a schematic view illustrating an example of the structure of afour-color separation prism;

FIG. 4 is a graph illustrating an example of spectral characteristics ofthe four-color separation prism;

FIG. 5 is a block diagram illustrating an example of the configurationof an endoscopic system in the first exemplary embodiment;

FIG. 6 shows schematic views illustrating an example of an image whichis displayed on a display in a dual output mode;

FIG. 7 is a schematic view illustrating an example of an image which isdisplayed on the display in a superimposed output mode; and

FIG. 8 is a graph illustrating spectral characteristics of a three-colorseparation prism.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an exemplary embodiment of this disclosure will bedescribed with reference to the accompanying drawings.

Circumstances for obtaining an exemplary embodiment of this disclosurewill be described.

In an operation in which an endoscope is used, a fluorescent substancecalled indocyanine green (ICG) is injected into the body, and a site(diseased site) (for example, a tumor) containing the excessivelyaccumulated fluorescent substance is irradiated with near-infraredlight, and an image of a site containing the diseased site is captured.The ICG is a substance that emits near-infrared fluorescent light havinga longer wavelength (for example, light having a peak wavelength of 835nm) when the ICG is excited by near-infrared light (for example, lighthaving a peak wavelength of 805 nm or 750 nm to 810 nm).

When one-plate camera with one image sensor receives light containing anIR component, and captures an image of a diseased site, a light incidentsurface of the image sensor is provided with four divided filters forred (R), green (G), blue (B), and IR components. Therefore, it isnecessary to increase the size of the image sensor to obtain desiredcolor reproductivity and desired resolution. As a result, a one platecamera can hardly be applied to an endoscope.

As illustrated in an endoscopic system disclosed in Japanese PatentUnexamined Publication No. 2013-116353, when a three plate camera usinga three-color separation prism receives light containing the IRcomponent, and captures an image of a diseased site, as illustrated inFIG. 8, the signal strength of the IR component (for example, lighthaving a wavelength of 800 nm or greater) is low.

FIG. 8 is a graph illustrating spectral characteristics of a three-colorseparation prism. In FIG. 8, the vertical axis represents thetransmittance of each color, and the horizontal axis represents thewavelength. The transmittance is equivalent to a ratio between theamount of light incident to each of prisms for R, G, and B componentsand the amount of light incident to image elements corresponding to theprisms. h11 represents the transmittance of R component light. h12represents the transmittance of G component light. h13 represents thetransmittance of B component light. h11 also contains the transmittanceof IR component light.

As illustrated in FIG. 8, the IR component light is acquired by theimage sensor receiving the R component light (refer to the waveformh11), but the transmittance of the IR component (for example, acomponent having a wavelength of 800 nm or greater) is low compared tothe transmittances of the R, G, and B component light. Therefore, thesignal strength of the IR component is low, and an image (IR image)obtained using the IR component becomes blurred.

In contrast, when the endoscopic system disclosed in Japanese PatentUnexamined Publication No. 2013-116353 amplifies the IR component toincrease the signal strength of the IR component, an image becomesblurred, or noise is emphasized. Therefore, the image quality of an IRimage is degraded. Accordingly, it is difficult to observe a desiredsite (diseased site) containing the IR component in the image obtainedusing the amplified IR component.

Hereinafter, an endoscope and an endoscopic system by which it ispossible to improve image quality of an image to which an infrared lightcomponent is added will be described.

The endoscope in the following exemplary embodiments is used to observea site (object) in the body, for example, in the abdominal cavity.

First Exemplary Embodiment Configuration of Endoscope

FIG. 1 is a schematic view illustrating the exterior of endoscope 10 ina first exemplary embodiment. FIG. 2 is a schematic view illustratingthe configuration of endoscope 10. Endoscope 10 is a medical instrumentwhich a user can handle with one hand. Endoscope 10 is configured toinclude scope 11; mounting adapter 12; relay lens 13; camera head 14;operation switch 19; and light source connector 18.

Scope 11 is a main part of a rigid endoscope, which is inserted into thebody, and is an elongated light guiding member capable of guiding lightfrom a proximal end to a distal end thereof. Scope 11 includesimage-capturing window 11 z at the distal end thereof; an optical fiberthrough which an optical image incident via the image-capturing window11 z is transmitted; and an optical fiber guiding light L, which isintroduced via light source connector 18, to the distal end.Image-capturing window 11 z is made of an optical material such asoptical glass or optical plastic.

Mounting adapter 12 is a member for mounting scope 11 on camera head 14.Various scopes can be attachably and detachably mounted on mountingadapter 12. Light source connector 18 is mounted on mounting adapter 12.

Light source connector 18 introduces illumination light for illuminatinga site (diseased site or the like) in the body from a light sourceapparatus (not illustrated). The illumination light contains visiblelight and IR light. Light introduced to light source connector 18 isguided to the distal end of scope 11 via scope 11, and a site (diseasedsite or the like) in the body is irradiated with the light viaimage-capturing window 11 z. For example, a light source is an LED lightsource. The light source may be a xenon lamp, a halogen lamp, or thelike instead of an LED light source.

Relay lens 13 converges the optical image, which is transmitted viascope 11, on an image-capturing surface. Relay lens 13 includes multiplelenses, and adjusts the focal point and the magnification ratio bymoving the lenses according to the amount of operation of operationswitch 19.

Camera head 14 includes a housing which the user can grasp with a hand;four-color separation prism 20 (refer to FIG. 3); four image sensors230, 231, 232, and 233 (refer to FIG. 3); and electronic substrate 250(refer to FIG. 5).

Four-color separation prism 20 is a four-plane prism separating thelight converged by relay lens 13 into three primary colors of light (Rlight (R component), G light (G component), and B light (B component))and IR light (IR component). Image sensors 230 to 233 convert opticalimages, which are separated by four-color separation prism 20 and formedon the image-capturing surfaces, into image signals (electricalsignals).

A charge coupled device (CCD), a complementary metal oxide semiconductor(CMOS), or the like is used as image sensors 230 to 233.

Four image sensors 230 to 233 are sensors respectively dedicated toreceive IR component light, B component light, R component light, and Gcomponent light. Therefore, unlike a one plate camera receiving IRcomponent light, R component light, G component light, and B componentlight via one image sensor, a small size sensor can be adopted as eachindividual image sensor. A ⅓ type (4.8 mm×3.6 mm) size image sensor isused. A one plate camera requires at least a ⅔ type (8.8 mm×6.6 mm) sizeimage sensor.

A signal output circuit outputting a signal by a low-voltagedifferential signaling (LVDS) method, a timing generator circuit (TGcircuit), and the like are mounted on electronic substrate 250 (refer toFIG. 5).

The signal output circuit outputs pulse type of RGB and IR signals forimages captured by image sensors 230 to 233 by the low-voltagedifferential signaling (LVDS) method. The TG circuit supplies timingsignals (synchronous signals) to inner components of camera head 14. TheRGB signal is a signal containing at least one of the R, G, and Bcomponents.

Signal cable 14 z for transmitting an image signal to camera controlunit (CCU) 30 (to be described later) is mounted on camera head 14.

Configuration of Four-Color Separation Prism

FIG. 3 is a view illustrating an example of the structure of four-colorseparation prism 20.

Four-color separation prism 20 separates incident light guided by relaylens 13 into three primary colors (R, G, and B components) of light, andIR component light. IR separation prism 220, blue color separation prism221, red color separation prism 222, and green color separation prism223 are sequentially assembled in four-color separation prism 20 inoptical axial directions.

IR image sensor 230 is disposed to face light emitting surface 220 c ofIR separation prism 220. Blue color image sensor 231 is disposed to facelight emitting surface 221 c of blue color separation prism 221. Redcolor image sensor 232 is disposed to face light emitting surface 222 cof red color separation prism 222. Green color image sensor 233 isdisposed to face light emitting surface 223 c of green color separationprism 223.

Image sensors 230 to 233 are CCD image sensors or CMOS image sensorsincluding pixels arrayed in horizontal (H) and vertical (V) directions.Image sensors 230 to 233 convert optical images, which are formed on theimage-capturing surfaces by the separated IR, R, G, and B componentlight, into electrical signals.

Light is incident to light incident surface 220 a of IR separation prism220. The light is reflected by reflective surface 220 b facing lightincident surface 220 a. All the reflected light is then reflected at theboundary of light incident surface 220 a of IR separation prism 220,emitted from light emitting surface 220 c facing light incident surface220 a, and incident to IR image sensor 230. IR reflective film 240 isformed on reflective surface 220 b by vapor deposition. IR separationprism 220 reflects the IR component light contained in the incidentlight, and allows the other component light (B, R, and G componentlight) to be transmitted therethrough. The light reflected by reflectivesurface 220 b and light incident surface 220 a is incident to andreceived by IR image sensor 230. As such, IR separation prism 220 isformed in order for light to travel through IR separation prism 220.

The light (incident light) transmitted through IR separation prism 220is incident to light incident surface 221 a of blue color separationprism 221. The light is reflected by reflective surface 221 b facinglight incident surface 221 a. All the reflected light is then reflectedat the boundary of light incident surface 221 a of blue color separationprism 221, emitted from light emitting surface 221 c facing lightincident surface 221 a, and incident to blue color image sensor 231.Blue color reflective film 241 is formed on reflective surface 221 b byvapor deposition. Blue color separation prism 221 reflects the Bcomponent light contained in the incident light, and allows the othercomponent light (R and G component light) to be transmittedtherethrough. The light reflected by reflective surface 221 b and lightincident surface 221 a is incident to and received by blue color imagesensor 231. As such, blue color separation prism 221 is formed in orderfor light to travel through blue color separation prism 221.

The light (incident light) transmitted through blue color separationprism 221 is incident to light incident surface 222 a of red colorseparation prism 222. The light is reflected by reflective surface 222 bfacing light incident surface 222 a. All the reflected light is thenreflected at the boundary of light incident surface 222 a of red colorseparation prism 222, emitted from light emitting surface 222 c facinglight incident surface 222 a, and incident to red color image sensor232. Red color reflective film 242 is formed on reflective surface 222 bby vapor deposition. Red color separation prism 222 reflects the Rcomponent light contained in the incident light, and allows the othercomponent light (G component light) to be transmitted therethrough. Thelight reflected by reflective surface 222 b and light incident surface222 a is incident to and received by red color image sensor 232. Assuch, red color separation prism 222 is formed in order for light totravel through red color separation prism 222.

The light (incident light) transmitted through red color separationprism 222 is incident to light incident surface 223 a of green colorseparation prism 223, emitted from light emitting surface 223 c facinglight incident surface 223 a, and then incident to green color imagesensor 233. As such, green color separation prism 223 is formed in orderfor light to travel through green color separation prism 223.

IR image sensor 230 may output an electrical signal having each pixelvalue (signal level) without being processed, or may perform an H/Vpixel addition process by which the pixel values of pixels adjacent toeach other in the horizontal (H) and vertical (V) direction are addedtogether, and output an electrical signal having a pixel value obtainedby the H/V pixel addition process.

When the H/V pixel addition process is performed, the pixel value of theIR component in IR image sensor 230 is changed to “120” (=30×4) fromapproximately “30”.

According to endoscope 10 in which IR image sensor 230 is independentlyprovided in the exemplary embodiment, the pixel value of the IRcomponent is changed to 3 to 12 times the pixel value (for example,approximately “10”) of the IR component in the related art.

In the exemplary embodiment, the pixel values of B image sensor 231, Rimage sensor 232, and G image sensor 233 are deemed to be approximately“100”. When the H/V pixel addition process is performed, the signallevel of each of the R, G, and B components and the signal level of theIR component become equal to each other, and a user can easily observean RGB image and an IR image. The RGB image is an image obtained from atleast one signal of R, G, and B component signals. The IR image is animage obtained from an IR component signal.

Spectral Characteristics of Four-Color Separation Prism

FIG. 4 is a graph illustrating an example of spectral characteristics offour-color separation prism 20. In FIG. 4, the vertical axis representsthe transmittance (%) which is equivalent to a ratio between the amountof light incident to the prisms and the amount of light incident toimage sensors 230 to 233 corresponding to the prisms. In FIG. 4, thehorizontal axis represents the wavelength (nm) of light incident to eachof image sensors 230 to 233.

In FIG. 4, waveform h1 (illustrated by the solid line) representsspectral characteristics of IR component light incident to IR imagesensor 230. The IR component light contained in the light incident tofour-color separation prism 20, which is incident to IR image sensor230, has a waveform with a wavelength of 800 nm to 1000 nm having a peaktransmittance of approximately 70% in the vicinity of a wavelength of900 nm.

Waveform h2 (illustrated by the alternate long and short-dashed line)represents spectral characteristics of the R component light incident tored image sensor 232. The R component light incident to red image sensor232 has a waveform having a peak transmittance of approximately 80% inthe vicinity of a wavelength of 600 nm.

Waveform h3 (illustrated by the dotted line) represents spectralcharacteristics of the B component light incident to blue image sensor231. The B component light incident to blue image sensor 231 has awaveform, the peak transmittance of which exceeds 60% in the vicinity ofa wavelength of 450 nm.

Waveform h4 (illustrated by the alternating one long and twoshort-dashed line) represents spectral characteristics of the Gcomponent light incident to green image sensor 233. The G componentlight incident to green image sensor 233 has a waveform having a peaktransmittance of approximately 90% in the vicinity of a wavelength of530 nm.

As such, the transmittance of all the IR, R, B, and G component lightseparated by four-color separation prism 20 exceeds 60%. Accordingly,the pixel values of the IR, R, B, and G components are suitably obtainedwithout considerably amplifying the IR component signal. As a result,when an image of a diseased site is captured, the color reproductivityof the captured image containing the IR component is improved.

Configuration of Endoscopic System

FIG. 5 is a block diagram illustrating the configuration of endoscopicsystem 5. Endoscopic system 5 is configured to include endoscope 10; CCU30; and display 40. Camera head 14 of endoscope 10 includes four-colorseparation system 20 and image sensors 230, 231, 232, and 233. In FIG.5, camera head 14 further includes element drivers 141 i, 141 r, 141 b,and 141 g; drive signal generator 142; synchronous signal generator 143;and signal output 145.

Element driver 141 i drives image sensor 230 according to a drivesignal. Element driver 141 r drives image sensor 231 according to adrive signal. Element driver 141 b drives image sensor 232 according toa drive signal. Element driver 141 g drives image sensor 233 accordingto a drive signal.

Drive signal generator 142 generates a drive signal for each of elementdrivers 141 i, 141 r, 141 b, and 141 g. Synchronous signal generator 143is equivalent to a timing generator (TG) open-path from the perspectiveof function, and supplies a synchronous signal (timing signal) to drivesignal generator 142 and the like.

Signal output 145 transmits electrical signals from image sensors 230,231, 232, and 233 to CCU 30 via signal cable 14 z by the LVDS method.Signal output 145 may transmit a synchronous signal from synchronoussignal generator 143 to CCU 30 via signal cable 14 z. Signal output 145may transmit an operation signal from operation switch 19 to CCU 30 viasignal cable 14 z. Signal output 145 is equivalent to a signal outputcircuit from the perspective of function.

CCU 30 realizes various functions by executing a program held in aninternal memory of CCU 30 or an external memory (not illustrated). Thevarious functions include the functions of RGB signal processor 22, IRsignal processor 23, and output 28.

RGB signal processor 22 converts electrical signals for the B, R, and Gcomponents from image sensors 231, 232, and 233 into image signals whichcan be displayed on display 40, and outputs the converted image signalsto output 28.

IR signal processor 23 converts an electrical signal for the IRcomponent from image sensor 230 into an image signal, and outputs theconverted image signal to output 28. IR signal processor 23 may includegain adjustor 23 z. Gain adjustor 23 z adjusts a gain when an electricalsignal for the IR component from IR image sensor 230 is converted intoan image signal. Gain adjustor 23 z may perform adjustment such that thesignal strength of the RGB component image signal is substantially thesame as the signal strength of the IR component image signal.

A user can reproduce an IR image having arbitrary strength with respectto an RGB image using gain adjustor 23 z. Instead of the gain of theelectrical signal for the IR component being adjusted, or together withthe adjustment of the gain of the electrical signal for the IRcomponent, RGB signal processor 22 may adjust the gain of the electricalsignals for the RGB component.

During signal processing, RGB signal processor 22 and IR signalprocessor 23 receive a synchronous signal from synchronous signalgenerator 143, and are operated according to the synchronous signal.Accordingly, the R, G, and B color component images and the IR componentimage are adjusted such that there is no timing offset therebetween.

Output 28 outputs at least one of the R, G, and B color component imagesignals and the IR component image signal to display 40 according to thesynchronous signal from synchronous signal generator 143. Output 28outputs an image signal based on either a dual output mode or asuperimposed output mode.

In the dual output mode, output 28 outputs RGB image G1 and IR image G2(refer to FIG. 6) on separate screens at the same time. In the dualoutput mode, a user can observe diseased site tg while comparing the RGBimage and the IR image on the separate screens to each other.

In the superimposed output mode, output 28 outputs combined image GZ inwhich an RGB image and an IR image are superimposed on each other. Inthe superimposed output mode, a user can clearly observe diseased sitetg that emits fluorescent light in the RGB image due to ICG and IR light(illumination light)

In this example, a processor in CCU 30 processes RGB signal processor22, IR signal processor 23, and output 28 software-wise in collaborationwith the memory; however, each of RGB signal processor 22, IR signalprocessor 23, and output 28 may be formed by dedicated hardware.

The screen of display 40 displays an image of an object (for example,diseased site tg), which is captured by endoscope 10 and output from CCU30, based on an image signal from CCU 30. In a dual output mode, display40 divides a screen into multiple screens (for example, two screens),and displays RGB image G1 and IR image G2 side by side on the respectivescreens (refer to FIG. 6). In a superimposed output mode, display 40displays combined image GZ, in which RGB image G1 and IR image G2 aresuperimposed on each other, on one screen (refer to FIG. 7).

In endoscopic system 5, indocyanine green (ICG) (fluorescent substance)may be injected into the body, a site (diseased site) (for example,tumor) in the body containing the excessively accumulated fluorescentsubstance may be irradiated with near-infrared light, and an image ofthe site may be captured using endoscope 10.

Light L introduced to light source connector 18 by the user's operationof operation switch 19 is guided to the distal end of scope 11,projected onto a site containing a diseased site and the surroundingsthereof from image-capturing window 11 z, and illuminates the site.Light reflected by the diseased site is guided to a rear end of scope 11via image-capturing window 11 z, converged by relay lens 13, andincident to four-color separation prism 20 of camera head 14.

IR component light separated from the incident light by IR separationprism 220 is captured as an infrared light component of an optical imageby IR image sensor 230 of four-color separation prism 20. B componentlight separated by blue color separation prism 221 is captured as a bluecolor component of an optical image by blue image sensor 231. Rcomponent light separated by red color separation prism 222 is capturedas a red color component of an optical image by red image sensor 232. Gcomponent light separated by green color separation prism 223 iscaptured as a green color component of an optical image by green imagesensor 233.

An electrical signal for the IR component converted by IR image sensor230 is converted into an image signal by IR signal processor 23 in CCU30, and is output by output 28. Electrical signals for the B, R, and Gcomponents converted by visible-light image sensors 231, 232, and 233are converted into image signals by RGB signal processor 22 in CCU 30,and are output by output 28. The IR component image signal, and the B,R, and G component image signals are output to display 40 in asynchronous mode.

When output 28 is set to a dual output mode, display 40 displays RGBimage G1 and IR image G2 on two screens at the same time. FIG. 6 showsschematic views illustrating images displayed on display 40 in a dualoutput mode. RGB image G1 is a color image obtained by irradiating asite containing diseased site tg with visible light and capturing animage of the site. IR image G2 is a black and white image (can be set toan arbitrary color) obtained by irradiating a site containing diseasedsite tg with IR light and capturing an image of the site.

When output 28 is set to a superimposed output mode, display 40 displayscombined image GZ in which RGB image G1 and IR image G2 are superimposed(combined together) on each other. FIG. 7 is a schematic viewillustrating an image displayed on display 40 in a superimposed outputmode.

Effects

Four-color separation prism 20 is used in endoscope 10, and IR imagesensor 230 receives IR light emitted from IR separation prism 220 havinga high transmittance with respect to IR light. Therefore, in endoscope10, the amount of IR light received can be increased. As a result, it isnot necessary to excessively amplify an IR component signal, and it ispossible to suppress degradation of quality of an image to which the IRcomponent is added and which is captured by endoscope 10.

It is possible to reduce the size of an image sensor compared to animage sensor in a one plate camera, and to reduce the size of endoscope10 by using four-color separation prism 20. The size of an image sensorin a one plate camera is 1 inch or 38 mm, and the size of each of imagesensors 230 to 233 in the exemplary embodiment is less than or equal to⅓ inch.

Since an IR cut filter is not used in four-color separation prism 20,endoscopic system 5 is capable of outputting an RGB image and an IRimage at the same time. Therefore, a user can confirm the entire sitecontaining a diseased site of a patient in the RGB image, and thediseased site emitting fluorescent light in the IR image, and easilyrecognize the position of the diseased site in the surroundings thereof.The RGB image is an RGB component image, and the IR image is an IRcomponent image.

IR image sensor 230 converting IR component light into an electricalsignal may perform an H/V pixel addition process, and output anelectrical signal having an added pixel value. Accordingly, endoscope 10is capable of further increasing the signal strength of the IRcomponent, and further emphasizing an IR component image displayed ondisplay 40, and a user can easily recognize a diseased site.

In endoscopic system 5, the gain may be adjusted such that the signalstrength of each of the R, G, and B components and the signal strengthof the IR component are substantially equal to each other. In this case,it is possible to set the pixel value of each of the R, G, and Bcomponents to be equal to the pixel value of the IR component, and toobtain an easy-to-see image.

In endoscopic system 5, the gain may be adjusted such that there is adifference between the signal strength of each of the R, G, and Bcomponents and the signal strength of the IR component. In this case,endoscopic system 5 is capable of displaying an RGB image and an IRimage having a user's desired image quality.

When four-color separation prism 20 is used, the signal strength of theIR component incident to the IR image sensor is increased compared towhen a three-color separation prism is used. Therefore, the differencebetween the pixel value of the RGB component and the pixel value of theIR component is decreased, and thus it is possible to reproducewell-balanced RGB and IR component colors without excessively amplifyingan electrical signal output from IR image sensor 230 using CCU 30.Accordingly, in endoscopic system 5, an image containing clear RGB andIR components is obtained while the amplification of noise issuppressed.

When an RGB image and an IR image are displayed on two screens at thesame time, a user can compare and confirm both images, and userfriendliness is improved.

When an RGB image and an IR image are disposed on one screen while beingsuperimposed on each other, a user can confirm an RGB component imageand an IR component image in one image, and user friendliness isimproved.

Other Exemplary Embodiments

The first exemplary embodiment has been described as an example of thetechnology in this disclosure. However, the technology in thisdisclosure is not limited to the first exemplary embodiment, and can beapplied to exemplary embodiments realized by making changes,replacements, additions, omissions, or the like to the first exemplaryembodiment.

In the first exemplary embodiment, a rigid endoscope is exemplified asendoscope 10; however, another rigid endoscope with a differentconfiguration or a flexible endoscope may be used insofar as four-colorseparation prism 20 is used.

In the first exemplary embodiment, ICG as an example of an opticalcontrast agent is injected into the living body; however, opticalcontrast agents other than ICG may be injected into the living body. Inthis case, spectral characteristics of non-visible light in thewavelength region may be determined according to the wavelength ofexcitation light for exciting the optical contrast agent.

In the first exemplary embodiment, a medicine emitting fluorescent lightin the wavelength region of infrared light is used; however, a medicineemitting fluorescent light in the wavelength region of ultraviolet lightmay be used. Also in this case, similar to the case in which an opticalcontrast agent emitting fluorescent light in the near-infrared region isused, an endoscope is capable of capturing an image of a diseased siteemitting fluorescent light.

In the first exemplary embodiment, IR separation prism 220, blue colorseparation prism 221, red color separation prism 222, and green colorseparation prism 223 are exemplarily disposed in four-color separationprism 20 sequentially from a light incidence side; however, anothersequence of disposition may be adopted.

In the first exemplary embodiment, CCU 30 is described as an example ofa processor. A processor may have any physical configuration insofar asthe processor is capable of controlling endoscopic system 5.Accordingly, a processor is not limited to CCU 30. When programmable CCU30 is used, it is possible to change process content by changing aprogram, resulting in an improvement in the degree of freedom indesigning a processor. A processor may be formed of one semiconductorchip, or may be physically formed of multiple semiconductor chips. Whena processor is formed of multiple semiconductor chips, control in thefirst exemplary embodiment may be realized by the separate correspondingsemiconductor chips. In this case, it can be deemed that one processoris formed of the multiple semiconductor chips. A processor may be formedof a member (capacitor or the like) having a function different fromthat of a semiconductor chip. A processor may be formed of onesemiconductor chip by which the function of a processor and otherfunctions are realized. When a programmable circuit is mounted onelectronic substrate 250, it is possible to change process content bychanging a program. The number of circuits may be one, or more than one.

What is claimed is:
 1. An endoscope comprising: a four-color separationprism configured to separate light from an object into three primarycolors of light and infrared light; four image sensors configured toconvert optical images of the separated three primary colors of lightand an optical image of the separated infrared light into electricalsignals; and an output device configured to output the convertedelectrical signals.
 2. The endoscope of claim 1, wherein the imagesensor adds the pixel values of adjacent pixels together when convertingthe optical image of the infrared light into the electrical signal usingmultiple pixels, and wherein the output device outputs an electricalsignal having an added pixel value.
 3. An endoscopic system including anendoscope, a processor, a memory, and a display, wherein the endoscopeincludes a four-color separation prism separating light from an objectinto three primary colors of light and infrared light, four imagesensors converting optical images of the separated three primary colorsof light and an optical image of the separated infrared light intoelectrical signals, and an output device outputting the convertedelectrical signals to the processor, wherein in collaboration with thememory, the processor converts a first electrical signal, which isconverted from each of the optical images of the three primary colors oflight, into a first image signal, and a second electrical signal, whichis converted from the optical image of the infrared light, into a secondimage signal, and wherein the display displays an image based on thefirst image signal and the second image signal.
 4. The endoscopic systemof claim 3, wherein in collaboration with the memory, the processorperforms adjustments such that the signal strength of the first imagesignal is substantially equal to the signal strength of the second imagesignal.
 5. The endoscopic system of claim 3, wherein the displaydisplays the first image signal and the second image signal at the sametime.
 6. A image display method in an endoscopic system including anendoscope, a processor, a memory, and a display, wherein the endoscopeseparates light from an object into three primary colors of light andinfrared light, converts optical images of the separated three primarycolors of light and an optical image of the infrared light intoelectrical signals, and outputs the converted electrical signals to theprocessor, wherein in collaboration with the memory, the processorconverts a first electrical signal, which is converted from each of theoptical images of the three primary colors of light, into a first imagesignal, and converts a second electrical signal, which is converted fromthe optical image of the infrared light, into a second image signal, andwherein the display displays an image based on the first image signaland the second image signal.
 7. The image display method in anendoscopic system of claim 6, wherein in collaboration with the memory,the processor performs adjustment such that the signal strength of thefirst image signal is substantially equal to the signal strength of thesecond image signal.